1. Field of the Invention
The invention relates to a method of recognizing speech pauses from the short-time spectrum of a speech signal which may have noise signals superposed on it.
2. Description of the Related Art
Methods of this type are, for example, the prerequisite for the suppression of noise signals when telephone calls are made from an environment with acoustic disturbances. During the speech pauses characteristic parameters of the noise signal are measured and employed, before transmission, to filter out the noise substantially wholly from the signal to be transmitted, using adaptive filters.
German Patent 24 55 477 and the corresponding British Pat. No. 1,515,937, published June 28, 1978, disclose in, column 10 an analog technique for recognition of speech pauses, which is based on the following method: the speech signal is divided into sections of equal lengths and a voltage value is obtained for each section by means of rectification and deriving the mean value, this voltage value being proportional to the average sound volume of the section. Finally, by deriving the mean value of several speech sections a further voltage value is determined, which is proportional to the average loudness of the conversation. By comparing these two mean values it is determined whether a particular section is associated with a speech pause or not.
In the said method of speech pause recognition no account is inter alia taken of the fact that, for example, during continuing speech there are unvoiced intervals which result in an almost total power reduction in the speech signal and the relevant speech sections are therefore erroneously recognized as speech pauses. Such faulty decisions occur in the prior art method more frequently as the extent to which noise signals are superposed on the speech signal increases.